package 过河卒;

import java.util.Scanner;

public class Main {
    static int N = 25;
    static long[][] f = new long[N][N];

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int n = in.nextInt() + 1;
        int m = in.nextInt() + 1;
        int a = in.nextInt() + 1;
        int b = in.nextInt() + 1;
        f[0][1] = 1;
        for (int i = 1; i <= n; i++) {
            for (int j = 1; j <= m; j++) {
                if(i == a && j == b){
                    continue;
                }
                if (i != a && j != b && Math.abs(i - a) + Math.abs(j - b) == 3) {
                    continue;
                }
                f[i][j] = f[i - 1][j] + f[i][j - 1];
            }
        }
        System.out.println(f[n][m]);
    }
}
